Osteomyelitis: Making the Diagnosis

Osteomyelitis – Making the Diagnosis

By Ben Cooper MD
Chief Resident, UTSW / Parkland Memorial Hospital

Edited by Alex Koyfman MD (@EMHighAK) and Stephen Alerhand MD

Featured on #FOAMED REVIEW 38TH EDITION – Thank you to Michael Macias from emCurious (@EMedCurious) for the shout out!

Patient Case

A 55 year-old male with diabetes status-post left trans-metatarsal foot amputation presents to the ED with a 3-week history of a progressive foot ulcer. He has lost feeling to his lower extremities, but denies purulent drainage from the wound. There have been no systemic symptoms. His vitals are all within normal limits, and physical exam reveals a 3 cm diameter ulcer overlying the prior amputation site. A plain film is obtained and shown below.

The x-ray is read as no focal demineralization to suggest osteomyelitis. Laboratory results reveal an ESR of 81, CRP 5, and WBC 8K. The patient was admitted for concern for osteomyelitis, which a subsequent MRI study confirmed. The patient was started on Doxycycline and Augmentin, then instructed to continue taking these antibiotics for 6 weeks with regular podiatry appointments. Ultimately, the patient had a femoral-femoral bypass and continues to struggle with serial infections.

Background

This is an all-too familiar scenario in patients with diabetic foot ulcers. Lack of sensation and poor vascularity creates a nice culture agar, and osteomyelitis seems imminent. This article will explore the tools that the Emergency Physician has to make the diagnosis and potentially save a limb.

In the patient population at Parkland, osteomyelitis (OM) usually results from direct extension of adjacent soft tissues (i.e. diabetic foot ulcers, or sacral decubitus ulcers), but can also result from hematogenous spread or direct inoculation as a result of trauma or surgery. Given the lack of sensitive physical exam findings, and the unavailability of time-consuming imaging modalities in the ED (magnetic resonance and/or bone scintigraphy), OM can be a difficult and sometimes elusive diagnosis to make in the ED setting.

Physical Exam

The physical exam is of somewhat limited value versus expected when evaluating patients with suspected OM. Probing to bone of diabetic foot ulcers has been found to have a sensitivity of 66%, and a specificity of 85% in a prospective study of 76 cases (1). An ulcer area larger than 2 cm² makes OM more likely (LR 7.2), while an ulcer less than 2 cm² makes it less likely (LR 0.48). The presence or absence of inflammatory signs such as erythema, edema, or purulence does not contribute to the probability of disease (10). All of these findings can aid the provider in making the diagnosis, but none have sufficient sensitivity to rule out disease.

(http://www.aotinc.net/aoti_diabetic_ulcer.html)

Imaging/Labs

With the limitations of physical exam in OM, plain film imaging and serum inflammatory markers are commonly obtained to aid the diagnosis. Findings suggestive of OM on radiography include cortical erosion, periosteal reaction, mixed lucency, and sclerosis. These signs may not be evident for up to 2 weeks into the infection (2). Sensitivity of plain radiographs (XR) has been reported between 43%-75% (2-5) for OM due to diabetic foot ulcers, but may be much less for other areas of OM (6).

Inflammatory markers including WBC, ESR, and CRP are routinely obtained for the evaluation of suspected OM. A review of the literature (for OM due to contiguous foot/ankle ulcers) found three studies that reported the sensitivity of ESR between 68-90% for varying cut-off values between 60 and 70 mm/hr, two that reported the sensitivity of CRP as 85% for cut-off values of 1.4 and 3.2 mg/dL, and two that reported the sensitivity of WBC as 41% and 75% for cut-off values of 11K and 14K, respectively (7-9). The largest of these studies included 34 patients with confirmed OM.

The sensitivity of MRI has been reported from 82 to 100%, and this is the diagnostic modality of choice (2) unless bone cultures can be obtained expeditiously – the gold standard. Typically, this is not something available in the ED for this diagnosis, and admission would be warranted.

Management

If the provider’s suspicion of OM is high, antibiotics are often initiated immediately in the ED prior to obtaining bone and/or wound cultures. Blood cultures are frequently obtained prior to the initiation of antibiotics despite low yields (11). If the patient is stable and does not meet criteria for sepsis, the provider should consider delaying antibiotics until obtaining wound and/or bone cultures.

Despite attempted conservative approaches to management of OM (i.e. antibiotics, surgical debridement), ultimate treatment often involves amputation. If antibiotics are initiated in the ED, consider coverage for MRSA, coagulase-negative staphylococci, and gram negatives (including pseudomonas). A typical regimen may be Vancomycin + Ciprofloxacin, and treatment is likely to span several weeks.

Summary

In summary, osteomyelitis is a difficult diagnosis to make. Certainly there are specific tests – i.e. probing to bone, findings on x-ray in the right clinical setting – but no test is sensitive enough to rule out. Inflammatory markers can again aid in raising suspicion, but are insensitive to rule out. Keep a high index of suspicion, and either admit for MRI, or secure good follow-up for patients with diabetic foot ulcers that present acutely or subacutely.

References / Further Reading:

1. Grayson ML, Gibbons GW, Balogh K, Levin E, Karchmer AW. Probing to bone in infected pedal ulcers. A clinical sign of underlying OM in diabetic patients. JAMA. 1995;273(9):721.
2. Pineda C, Espinosa R, Pena A. Radiographic imaging in OM: the role of plain radiography, computed tomography, ultrasonography, magnetic resonance imaging, and scintigraphy. Semin Plast Surg. 2009; 23(2): 80-89.
3. Shults DW,Hunter GC, McIntyre KE, Parent FN, Piotrowski JJ, Bernhard VM. Value of radiographs and bone scans in determining the need for therapy in diabetic patients with foot ulcers. Am J Surg. 1989 Dec;158(6):525-9.
4. Yuh WT,Corson JD, Baraniewski HM, Rezai K, Shamma AR, Kathol MH, Sato Y, el-Khoury GY, Hawes DR, Platz CE, et al. OM of the foot in diabetic patients: evaluation with plain film, 99mTc-MDP bone scintigraphy, and MR imaging. AJR Am J Roentgenol. 1989 Apr;152(4):795-800.
5. Larcos G, Brown ML, Sutton RT. Diagnosis of OM of the foot in diabetic patients: value of 111 In-leukocyte scintigraphy. AJR Am J Roentgenol 1991;157: 527–31.
6. Tumeh SS, Aliabadi P, Weissman BN, McNeil BJ. Disease activity in OM: role of radiography. Radiology. 1987;165(3):781.
7. Michail M, Jude E, Liaskos C, Karamagiolis S, Makrilakis K, Dimitroulis D, Michail O, Tentolouris N. The performance of serum inflammatory markers for the diagnosis and follow-up of patients with OM. Int J Low Extrem Wounds. 2013 Jun;12(2):94-9. doi: 10.1177/1534734613486152. Epub 2013 May 9.
8. Fleischer AE, Didyk AA, Woods JB, Burns SE, Wrobel JS, Armstrong DG. Combined clinical and laboratory testing improves diagnostic accuracy for OM in the diabetic foot. J. Foot Ankle Surg. 2009; 48 (1): 39–46.
9. Kaleta JL, Fleischli JW, Reilly CH. The diagnosis of OM in diabetes using erythrocyte sedimentation rate: a pilot study. J. Am. Podiatr. Med. Assoc. 2001; 91: 445–50.
10. Butalia B, et al. Does this Patient with Diabetes Have Osteomyelitis of the Lower Extremity? JAMA. 2008; 299(7):806-13.
11. http://www.acepnow.com/article/blood-culture-testing-send-samples-selectively-lower-costs-medico-legal-risk/
12. http://www.ncbi.nlm.nih.gov/pubmed/22224154
13. http://www.ncbi.nlm.nih.gov/pubmed/19380041
14. http://www.ncbi.nlm.nih.gov/pubmed/12563584